Staff members at numerous federal offices in Kentucky got quite a scare on Monday. Some found themselves reading a letter purporting to contain the deadly anthrax virus. Fortunately, it appears the letters are all part of a cruel hoax.

The letters showed up at federal courthouses and congressional offices across the state. Tests on the white powdery substance contained in the letters have turned up negative for anthrax.

In the course of its investigation, the FBI has narrowed its focus on an inmate in the Big Sandy federal prison in Martin County. The inmate reportedly told investigators that the substance was actually an artificial sweetener.

No word yet on what motivated the suspect to send the letters. Those offices that received the letters were evacuated and some people were taken to area hospitals. However, no one has shown any signs of illness related to exposure to the letters.